HI Josh,
It appears the Senior Discount shows up on some Italo routes sometimes but not all. For example, I tried Rome-Florence return April 15-18. The Senior rate was the last on the list for April 15, beneath "Extra Magic" (Extra magic is non-refundable and does not allow changes, whereas the Sr rate allowed some changes). There was no discount on the April 18 leg, which suggests that fare has sold out.
The Italo 2x1 offer notes the following: "50% discount compared to the Flex fare price, available for groups of 2 passengers traveling in Smart or Prima Business class. Offer valid until 22/03. Thereafter, it applies exclusively on 05/04 and 02/05." So maybe your dates don't work?
For the carta Freccia program: It's not that hard to get. When signing up, you have to click the box that says "I do not have a tax code." and indicate that your residence is abroad. Once you have a number (it comes instantly), you proceed with your booking. You have to enter your birthdate when signing up. I am guessing that the program will automatically recognize when a senior rate should apply. My birthdate doesn't quite qualify, so I can't see those rates. Perhaps someone else can confirm?
For comparison, Italo came out about 30 euros cheaper when I ran my test for similar departure times. But as I said, I can't generate the senior rate associated with the Freccia discount.
Hope this is helpful!